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Comment PDF Separation Processes

Scrubbers: Are You Ready?

By Joy LePree |

Most members of the highly regulated chemical process industries (CPI) are aware of the growing worldwide attention focused on the issues of climate change, air and water pollution and the supply and protection of natural resources. For this reason, air-pollution-control scrubbers play an integral role in most chemical processing facilities. However, the economic downturn caused many processors to shelve air-pollution-control projects during the past year. But with the recent hint of potential regulatory action in the air, it might be wise to dust off those project plans and take a look at the newest scrubbing technologies designed to help processors meet current and future air-pollution-control challenges and “green up” their scrubbing processes at the same time.

Next in the regulatory pipeline

While there is currently uncertainty in the area of upcoming CO2 legislation, experts in the industry suggest that there will be some new mandates regarding carbon capture technology in the future. “For this reason we see many processors interested in driving down emissions for CO2, as well as SO2, SO3 and NOx to significantly lower levels than where they currently operate,” says Tony Licata, vice president of Babcock Power Environmental (Worchester, Mass.; www.babcockpower.com).

Ammonium sulfate technology, which serves as an alternative to traditional wet fluegas desulfurization, uses aqueous or anhydrous ammonia to convert SO2 emissions into a high-quality, high-value commercial grade ammonium sulfate crop fertilizer
Marsulex Environmental Technologies.

In addition to CO2 legislation, a new proposed air-pollution rule that would significantly alter permissible air-pollution-control levels in the U.S. would require the installation of scrubbers on more than 200 cement kilns, according to Bob McIlvaine, president of the McIlvaine Co. (Northfield, Ill.; www.mcilvainecompany.com). “There would be new Maximum Achievable Control Technology (MACT) rules, which would result in scrubbers being placed in most cement plants,” he says.

Similarly, he says, MACT regulations regarding hydrochloric acid in power plants may result in the installation of new scrubbing technologies in these facilities. “It would be a ‘make lemons into lemonade’ situation because rather than removing the HCl and having it as a contaminant in wastewater that would require further treatment, we believe a two-stage scrubbing system that captures HCl in the first stage and SO2 in the second, allowing processors to make both hydrochloric acid and gypsum, is likely to become the technology of choice.”

McIlvaine says that while such a system would involve billions of dollars in investment, the technology already exists and is employed in Europe, which proves it is a viable solution to potential legislation in the U.S.

Other possible regulatory action to consider includes a revisit of the Boiler MACT by the U.S. Environmental Protection Agency (EPA; Washington, D.C.), says Kevin Moss, business development director, with Tri-Mer (Owosso, Mich.; www.tri-mer.com). He notes that while Boiler MACT was developed a few years ago, it was shelved because it was not being applied uniformly. “There’s been another round of EPA going back to formulate a new Boiler MACT. The regulation was released in April for comment and will likely be law by December 2010,” says Moss. The rule would give companies with boilers burning coal, wood or solid fuels three years to comply with the new MACT regulations.

And, aside from the possibility of new mandates concerning air pollution control, many industry experts get a sense of stricter enforcement on existing regulations. “What we are starting to see is a much more active EPA under this administration,” says Moss. “There’s more aggressive enforcement of laws already on the books, so now is a good time to start taking a serious look at air pollution control.”

New technologies deliver

For this reason, many scrubber manufacturers are bumping up their game and striving to improve existing technologies or develop new ones in an effort to meet or exceed today’s mandates, as well as any that are expected to come down the pike.

For example, to help with compliance of stricter Boiler MACT regulations, Tri-Mer is offering the Ultra-Temp Filtration (UTF) system. “We expect as they regulate particulate matter coming from boilers, they are likely to further regulate SO2, HCl and other acid gases,” says Moss.

UTF technology uses ceramic tube filters made of ductile ceramic fibers, which are able to handle the high temperatures (applications up to 1,000°F and temperature resistant up to 1,650°F) of boiler exhaust gases and filter the particulate down to very low levels. The system offers a very high efficiency and can handle even submicron particulate matter. The UTF system can also be employed for concurrent gas scrubbing, to remove acid gases through injection of a dry scrubbing agent, such as limestone or Na2HCO3.

Also intended to meet stricter regulations regarding acid gases is Babcock Power Environmental’s Turbosorp Dry Circulating fluid-bed scrubber for processes requiring dry technology. The system removes acid fluegas constituents, primarily SO2 and SO3, as well as mercury, HCl and HF from coal-fired boilers. Turbosorp is available for capacities up to 300 MW per turboreactor and is suited for facilities with sulfur contents below 3%. Acid gas removal efficiencies of 95 to 97% are typical.

The principal of the scrubbing technology is to bring high levels of solid recirculation, finely atomized water, hydrated lime and fluegas within a circular fluid-bed reactor. Lime and finely atomized water are injected independently into the turboreactor to lower fluegas temperature and enhance absorption capacity.

The fluid bed material is comprised of solids, including Ca(OH)2, fly ash from the combustion process and solid reaction products from the fluegas particulate-matter device. Upon leaving the turboreactor, the solids are separated from the fluegas in either a fabric filter baghouse or an electrostatic precipitator and recycled back to the reactor. Where mercury and dioxin removal are required, activated carbon can be injected into the turboreactor.

Envirofriendly systems

While the goal of all air pollution scrubbers is to save the environment from toxic gases and particulate matter (while helping the processor meet regulatory mandates), many scrubber manufacturers are working to make the scrubbing systems themselves as safe for the environment as is possible, while still producing results that meet or exceed current and expected regulations.

Bioscrubbers, one of the most common types of environmentally friendly scrubbing systems available, have been around for over 20 years, but have previously found only limited use in VOC (volatile organic compound) removal applications. “Bioscrubbers were thought to be a low-tech approach,” says Moss. “They simply weren’t able to get to high efficiencies and had a limited number of VOCs they could attack.”

However, recent technology upgrades have made this type of system more viable than ever before. For instance, Tri-Mer’s MultiPhase Bioscrubber overcomes the disadvantages of conventional bioscrubbers designed for the biological treatment of air pollutants by treating incoming contaminants in the phase (liquid or gas) in which the contaminant would normally reside, depending on its inherent properties.

For example, a highly volatile compound with low water solubility will concentrate in the bioscrubber gas phase, and will be treated mainly in the gas phase. Highly water-soluble compounds with low volatility will concentrate in the bioscrubber water phase and will be treated in the water phase. Most compounds with intermediate volatility and water solubility will be treated in both the gas and water phases, depending on their natural partitioning.

Conventional biofiltration systems attempt to treat all the contaminants in the gas phase, whereas a conventional bioscrubber delegates the treatment of the water-soluble fractions of the contaminants to an external treatment system, often with design flaws that can either partially re-entrain the contaminants into the ambient environment or allow the contaminants to accumulate and escape through the water.

None of the conventional systems are designed to handle particulate matter in the gas phase, treat condensables with high molecular weight, nor handle the dissipation of heat if the incoming stream is above the normal operating temperature of aerobic organisms (50 to 105°F).

However, the newer MutliPhase Bioscrubber system can handle much higher inlet temperatures from dryers. Often, exhausts from press vents and dryers are treated together, producing significant cost advantages.

Other advantages of the MultiPhase Bioscrubber technology include the ability to accommodate high particulate loads, compatibility with high inlet concentrations of VOCs, high efficiency removal, permanent ceramic media, automatic self cleaning and the ability to handle tars, waxes and heavy VOC compounds. Also, waste generation is minimal with no NOx compound creation.

Similarly, Duall Division of Met-Pro (Owosso, Mich.; www.dualldiv.com) has recently launched its line of Bio-Pro Scrubbers. These scrubbers are touted as being 100% environmentally friendly and are efficient at controlling and removing H2S emissions and odors. “The real drive toward improving and embracing bioscrubbers is the fact that you are using green technology versus chemicals,” says Greg Kimmer, vice president and general manager of Duall. “Not only is it a natural technology, but in this economic climate, it is efficient because you aren’t spending as much on chemicals.”

Duall’s Bio-Pro employs a state-of-the-art biotrickling filter technology in combination with a unique blend of micro-organisms to provide 99% H2S removal with a side range of inlet loadings and provides an environmentally safe byproduct.

Another environmentally friendly option comes from Purafil Environmental Systems (Doraville, Ga.; www.purafil.com). The Purafil ESD FOC-1, fiberglass Emergency Gas Scrubber (EGS) with Chlorosorb dry scrubbing medium uses a non-toxic, dry-scrubbing medium in place of a toxic, liquid caustic to neutralize gases in the event of an emergency situation. This medium’s “chemisorptive” process removes chlorine by means of adsorption and chemical reaction. Chlorine gas is trapped within the pellet where an irreversible chemical reaction changes the gases into harmless solids.

This type of emergency standby equipment is necessary for facilities that store large quantities of Cl2, typically in one or more one-ton cylinders to prevent accidental chemical releases. If a toxic gas release from a one-ton cylinder were to occur, the thermodynamic properties of Cl2 suggest that approximately 400 lb of liquid Cl2 would flash into vapor and the remaining contents of the cylinder would spill out as a liquid at its boiling point. According to the American Water Works Association’s Risk Management Program, the outer limit of the impact area, in a Cl2 release, is drawn at a five-mile radius in all directions from the point of impact.

Purafil’s dry chemical EGS is designed to contain the entire contents of a fully loaded one-ton Cl2 cylinder in a worst-case scenario. The EGS can neutralize an initial 400 lb in the first minute and any additional chlorine at a rate of 80 lb/min thereafter.

Ammonia scrubbing is also seeing a rise when compared to calcium-based technologies, since ammonia is carbon neutral. “Ammonia scrubbing doesn’t contribute incremental CO2 to the atmosphere,” notes Dave Olson, vice president of licensing and commercial operations with Marsulex Environmental Technologies (Lebanon, Pa.; www.marsulex.com). And, Marsulex Environmental’s new ammonia scrubber takes it even further. “It can be used to make and sell commercial grade fertilizer for more than it costs for the ammonia to make that fertilizer, so you can generate some revenue back to pay for other operating costs of the plant,” notes Olson.

In addition, the fertilizer made from Marsulex’s ammonium sulfate (AS) fluegas desulfurization (FGD) technology can be used to grow more plants and crops, especially those that are high in photosynthesis. “The so-called ‘C4 plants’ that are high in photosynthesis help with CO2 absorption from the atmosphere,” explains Olson. “So it’s a very efficient technology and very effective for the kind of environment we are looking at today.”

AS Technology, which serves as an alternative to traditional wet FGD, uses aqueous or anhydrous ammonia to convert SO2 emissions into a high-quality, high-value, commercial-grade ammonium-sulfate fertilizer. Most beneficial in power, petrochemical and industrial plants with higher sulfur fuels, proximity of navigable water or good rail access and locations with regional demand for high-quality crop fertilizer, the technology provides longterm environmental compliance and requires no chemical or byproduct waste handling. Every ton of NH3 used generates approximately four tons of ammonium sulfate fertilizer.

Other benefits include water-soluble chemistry that prevents internal build up, NH3 reagent with 98% removal efficiency with unlimited sulfur contents and the elimination of liability associated with waste product disposal.

While no one knows exactly what tomorrow’s regulatory environment will bring, the technologies to meet the likely mandates currently exist, making now the time to see what options are available and get the right one for your facility in place.


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Wet Scrubbers
Wet fluegas desulfurization (FGD), also known as wet-scrubbing, is a popular pollution-abatement technique for removing acid gases, such as SO2…

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